This invention relates to implantable stimulators generally, and to implantable defibrillators more particularly.
Over the past twenty years, there has been substantial work toward developing a practical, implantable defibrillator. However, several significant problems must still be overcome. Early conceptions of implantable defibrillators, such as disclosed in Pat. No. Re. 27,652, by Mirowski et al, envision a system employing a ventricular endocardial electrode and a plate electrode mounted to the heart directly, subcutaneously, or to the skin. However, it was recognized early on that a totally transvenous system would be desirable in order to simplify the use of implantable defibrillators. One such system is suggested in U.S. Pat. No. 3,942,536 by Mirowski et al, which discloses a transvenous lead having electrodes intended for location in the right ventricular apex and superior vena cava. Such systems were eventually tested in human beings, with some success. However, currently available commercial versions of implantable defibrillators employ epicardial patch electrodes in conjunction with transvenous electrodes.
While systems employing a transvenous endocardial electrode in combination with an epicardial patch electrode are workable, a thoracotomy is required in order to apply the epicardial electrode. It is generally believed that it would be highly desirable to produce an implantable defibrillator system which would entirely avoid the necessity of a thoracotomy, and there has been substantial work directed towards such systems, as disclosed in U.S. Pat. No. 4,727,877 issued to Kallok, and U.S. Pat. No. 4,708,145 issued to Tacker et al. Both the Tacker et al and Kallok patents disclose the use of a transvenous, two electrode lead in combination with a subcutaneous patch electrode.
Transvenous ventricular defibrillation electrodes are shown in the above-cited Mirowski patents and in the Tacker and Kallok patents cited above. Other endocardial defibrillation electrodes are disclosed in U.S. Pat. No. 4,481,953 issued to Gold et al, U.S. Pat. No. 4,161,952 issued to Kinney et al and U.S. Pat. No. 4,641,656 issued to Smits. The Kinney, Smits and Kallok patents also disclose transvenous defibrillation electrodes intended for use in or adjacent to the coronary sinus.